This invention relates to an improved cylinder lock construction having a plug which is removable by means of a proper pass key.
It has long been recognized that a cylinder lock having a removable plug is a desirable product. For example, one may remove the plug in order to substitute another plug having a different key bitting arrangement. Alternatively, the plug may need to be removed for repair. Various prior art patents teach such removable plug constructions including U.S. Pat. No. 4,398,405 issued Aug. 16, 1983 for a "Lock with Key Controlled Removable and Installable Plug and Key for Same" as well as U.S. Pat. No. 4,416,129 issued Nov. 22, 1983 for a "Cylinder Lock and Key Removable Plug". The text of the two patents referenced is incorporated by reference. The patents are believed typical of the prior art relating to the subject matter of the present invention.
With respect to both of the referenced patents, the removable plug includes a series of combinating tumblers in the form of disc tumblers which are spring biased into engagement with the cylinder to thereby lock the plug to the cylinder. The combinating tumblers may be translated to an unlocked position, permitting plug rotation relative to the cylinder, by insertion of a proper key that engages the combinating tumblers and moves them against the spring biasing force.
The removable plug also includes, typically, a control tumbler which is responsive to a special control key. The control tumbler is normally spring biased into an annular groove on the inside surface of the cylinder to prevent removal of the plug from the cylinder. Thus, the plug may be rotated but not removed. The control tumbler can be released from that groove or slot only when engaged and moved out of the groove by a particular control key. Insertion of the control key thus will move the control tumbler against the spring biasing force acting on that tumbler to effect removal of the tumbler from the annular groove and permitting consequent release of the plug from its associated cylinder.
The prior art teachings perform in a satisfactory manner. However, in the references identified, biasing means such as a spring is utilized to engage the control tumbler. In the event the spring breaks, the plug associated with the cylinder may be accidentally released. Additionally, the use of a spring in association with a control tumbler constitutes an extra part necessary for the operation of the lock.
The inventor has developed a removable plug, disc tumbler lock which eliminates the need for a spring biased control tumbler. The lock utilizes a cylindrical plug which may be inserted into a cylinder having a cylindrical passage for receipt of the plug. The external size or outside diameter of the cylinder for such a lock is often too great to be useful in certain applications. For example, filing cabinets often require a lock having relatively small external dimensions. One way to provide such a smaller lock is to merely make the plug, cylinder, tumblers and key smaller. However, this requires total retooling. Also, smaller tumblers are more difficult to handle during manufacture, and reduce the total number of key combinations practical compared with larger tumblers.
Thus, a need has developed for a combinating tumbler construction having smaller external dimensions which utilizes lock components from conventionally sized locks, particularly tumblers and associated keys. Moreover, such a lock should incorporate or retain all the features of conventional locks such as the capability of a removable plug. The present invention constitutes a construction which accomplishes this objective and other objectives.